The present invention relates to an electrolysis of sodium chloride by using a cation exchange membrane having excellent characteristics as a membrane for an electrolysis to produce sodium hydroxide in a cathode compartment and to produce chlorine in an anode compartment.
A diaphragm method has been known to produce sodium hydroxide under partitioning the anode compartment and the cathode compartment with a diaphragm.
In the diaphragm method, a diaphragm having high water permeability as an asbestos diaphragm is used. In order to prevent the reverse diffusion of OH ions from a cathode compartment to an anode compartment, an electrolysis is carried out under passing an aqueous solution of sodium chloride from the anode compartment to the cathode compartment. Accordingly, a large amount of sodium chloride is included in an aqueous solution of sodium hydroxide in the cathode compartment and a concentration of sodium hydroxide is low.
On the other hand, when an electrolysis of sodium chloride is carried by using a cation exchange membrane and feeding an aqueous solution of sodium chloride to the anode compartment, the diffusion of OH ions from the cathode compartment to the anode compartment can be effectively prevented and the movement of sodium chloride from the anode compartment to the cathode compartment can be substantially prevented in principal whereby sodium hydroxide having high purity can be produced in high current efficiency and the concentration of sodium hydroxide in a cathode compartment is increased in comparison with that of the conventional diaphragm method, advantageously. However, in a practice, it has not been found to obtain a cation exchange membrane which satisfactorily prevents the permeation of OH ions and is durable in severe conditions in the electrolytic cell.